Android Button 的回调机制分析

在我搜索学习回调机制时，找到这篇博客http://blog.csdn.net/xiaanming/article/details/17483273 ，它里面讲到Button是极好的回调机制的例子，于是我进行了深入的了解了一下，Button到底是怎样工作的

Button的一般设置形式：

    button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                
            }
        });

打开android.jar,在包android.widget找到类Button.class：

public class Button extends TextView {
    public Button(Context context) {
        this(context, null);
    }

    public Button(Context context, AttributeSet attrs) {
        this(context, attrs, com.android.internal.R.attr.buttonStyle);
    }

    public Button(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }
}

Button继承自TextView，继续在包内找类TextView.class：

public class TextView extends View implements ViewTreeObserver.OnPreDrawListener 

TextView继承自View，贴出与Button相关的代码：

 1 public class View implements Drawable.Callback, Drawable.Callback2, KeyEvent.Callback,
 2 AccessibilityEventSource {
 3 
 4 /**
 5      * Register a callback to be invoked when this view is clicked. If this view is not
 6      * clickable, it becomes clickable.
 7      *
 8      * @param l The callback that will run
 9      *
10      * @see #setClickable(boolean)
11      */
12     public void setOnClickListener(OnClickListener l) {
13         if (!isClickable()) {
14             setClickable(true);
15         }
16         getListenerInfo().mOnClickListener = l;
17     }
18 
19   /**
20      * Call this view's OnClickListener, if it is defined.  Performs all normal
21      * actions associated with clicking: reporting accessibility event, playing
22      * a sound, etc.
23      *
24      * @return True there was an assigned OnClickListener that was called, false
25      *         otherwise is returned.
26      */
27     public boolean performClick() {
28         sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
29 
30         ListenerInfo li = mListenerInfo;
31         if (li != null && li.mOnClickListener != null) {
32             playSoundEffect(SoundEffectConstants.CLICK);
33             li.mOnClickListener.onClick(this);
34             return true;
35         }
36 
37         return false;
38     }
39 
40   /**
41      * Call this view's OnClickListener, if it is defined.  Performs all normal
42      * actions associated with clicking: reporting accessibility event, playing
43      * a sound, etc.
44      *
45      * @return True there was an assigned OnClickListener that was called, false
46      *         otherwise is returned.
47      */
48     public boolean performClick() {
49         sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
50 
51         ListenerInfo li = mListenerInfo;
52         if (li != null && li.mOnClickListener != null) {
53             playSoundEffect(SoundEffectConstants.CLICK);
54             li.mOnClickListener.onClick(this);
55             return true;
56         }
57 
58         return false;
59     }
60 }